Vadim V. Silberschmidt

Bio: Vadim V. Silberschmidt is an academic researcher from Loughborough University. The author has contributed to research in topics: Machining & Materials science. The author has an hindex of 44, co-authored 543 publications receiving 8619 citations. Previous affiliations of Vadim V. Silberschmidt include University of Rhode Island & Universities UK.

ZigZagZ: Improving mechanical performance in extrusion additive manufacturing by nonplanar toolpaths

Abstract: This study investigates the effect of novel non-planar deposition methods in fused filament fabrication (FFF) additive manufacturing. A range of non-planar geometries were developed including a ZigZagZ sequence in which filaments were deposited as the nozzle moved in the X or Y direction while simultaneously zigzagging up-and-down i.e. in the Z direction. As a result, repeating non-planar layers were generated throughout the specimen’s geometry. The use of the ZigZagZ toolpath to deposit the material significantly improved the mechanical performance of parts manufactured by FFF in the Z-direction by up to 62% in strength, 123% in strain-at-fracture and 245% in toughness compared to an optimised conventional planar geometry. All specimens in the study had only a single filament through their thickness; they were specially developed to enable precise mechanical characterisation. This is the first work to have developed and analysed nonplanar deposition with cyclic nonplanar nozzle movement of a geometric length scale similar to the nozzle diameter. Three novel toolpath designs were developed for this study: (i) zigzag (ZZ), based on the aforementioned ZigZagZ deposition; (ii) up-down (UD) involving vertically deposited nonplanar bulges with interconnecting planar sections; (iii) forward-back (FB) employing the nozzle’s movement forward and backward during planar deposition to enhance the nozzle’s contact and promote the ploughing of the deposited filament. These designs - along with the conventional planar toolpath designs (original (OR)) - were characterised and their mechanical properties compared to generate new understanding about the impact of deposition with the Z coordinate varying along the path on performance. The geometrical outcomes of these different deposition strategies were analysed microscopically to assess the effects of nonplanar toolpaths on the filament-scale geometry. It was established that the ZZ strategies resulted in higher extruded-filament thickness compared to OR. Additionally, various ZZ designs were developed to understand the impact of the zigzag height-to-width ratio and size not only on mechanical properties, but also geometry and fracture path. Fractographic analysis indicated that nonplanar FFF extrusion promoted through-filament fracture, suggesting a reduced concentration of stresses at interlayer bonds by redirecting the load into the filament; this could contribute to the increased level of toughness observed in ZZ specimens. The understanding developed in this study is readily adaptable for the use in both single-wall and infill geometries to provide their improved mechanical performance. A broad range of potential industrial applications and research relevance resulting from the findings is discussed in addition to future development opportunities.

Grain features of SnAgCu solder and their effect on mechanical behaviour of micro-joints

Abstract: SnAgCu alloy, which promises compatible properties with Sn-Pb solder, has been identified as one of the most potential Lead-free solders for electronic interconnections. However, due to the miniaturization of solder joints, a micro-joint of this material contains only few grains. In this case, the mechanical behaviour of solder alloys shifts from the polycrystal-based to single-crystal based. Since P-Sn, the matrix of SnAgCu solder, has a contracted body-centred tetragonal structure, its grains are expected to have anisotropic properties, which are important, the reliability of a micro-joint. The present paper studies the inelastic anisotropic behaviour of this material. In order to analyse the effect of grain features, solder joints at different size are formed under the different cooling rate. An in-situ shear test is then performed to correlate the mechanical behavior of a joint to its microstructural features. The results show that the decrease in the joint's dimension results in the diminishment of the number of grains, and that the inelastic behaviour of SnAgCu grains is orientation-dependent.

Assessment of structural integrity of subsea wellhead system: analytical and numerical study

Abstract: Subsea wellhead systems exposed to severe fatigue loading are becoming increasingly a significant problem in offshore drilling operations due to their applications in wells with higher levels of pressure and temperature, situated at larger depths and in harsher environments. This has led to a substantial increase in the weight and size of offshore equipment, which, in combination with different loading conditions related to the environmental factors acting on the vessel and riser, has greatly increased the loads acting on subsea well systems. In particular, severe fatigue loading acting on the subsea wellhead system was detected. For this reason, a combined analytical and numerical study investigating the critical effect of crack depth on the overall structural integrity of subsea wellhead systems under cyclic loading was carried out. The study is based on a Linear Elastic Fracture Mechanics (LEFM) approach.

In-vitro experimental analysis and numerical study of temperature in bone drilling

Abstract: BACKGROUND: Bone drilling is a common practice of surgical treatments in orthopaedics and traumatology. Penetration of a high-speed drill into bone tissue is accompanied by generation of a significant amount of heat. Cooling of the drilling region is necessary to avoid potential risk of thermal damage to bone. OBJECTIVE: The purpose of this study was to measure and predict bone temperature by conducting experiments and numer- ical simulations using cooling by means of irrigation at two different temperatures. METHODS: A series of experiments and numerical studies were performed to investigate the effect of cooling conditions on the rise in bone temperature in drilling. The temperature increase in bone was assessed for different drilling speeds and feed rates in the presence irrigation at 5◦C and 25◦ C. RESULTS: Bone temperature was found to be strongly affected by the drilling parameters and cooling conditions. Irrigation with water at 5◦C kept bone temperature well below the thermal threshold level. CONCLUSION: This study strongly recommends the use of irrigation at lower temperature for safe surgical incision.

Patient-specific modelling of stent overlap: Lumen gain, tissue damage and in-stent restenosis.

Abstract: This paper investigates the effects of multiple stents, with and without overlap, on the outcome of stent deployment in a patient-specific coronary artery using the finite element method. Specifically, the objective of this study is to reveal the effect of stent overlap on lumen gain, tissue damage and in-stent restenosis in percutaneous coronary intervention. Based on intravital optical coherency tomography imaging, three-dimensional model of a specific patient's coronary artery was developed, with two constituent layers (media and adventitia) and plaque, using Mimics. Hyperelastic models with damage, verified against experimental results, were used to describe stress-stretch responses of arterial layers and plaque. Abaqus CAE was used to create the models for Resolute Integrity™ drug-eluting stents and tri-folded expansion balloons. The results showed that lumen gain was improved by the overlapping stents than a single stent after deployment; however, damage to the media layer was greater, promoting a higher rate of in-stent restenosis. Meanwhile, the lumen gain achieved with the non-overlapping stents was smaller than that with the overlapping ones, due to an increased recoiling effect. Also, non-overlapping stents induced more tissue damage and higher rate of in-stent restenosis than overlapping stents. With respect to long-term clinical outcomes, the study recommended the use of a single stent where possible or multiple stents with minimal overlaps to treat long or angulated lesions.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Effect of Temperature

Abstract: A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.